Originally Posted by Kevin_Hsu
Is the purple in the second graph with all of them time aligned but not EQ'd?
I apologize in advance for yet another super long post...
No. 2nd graph purple is with all 3 subs with no time alignment, inversion, or EQ applied; "as-is" if you will. The green line is after inverting sub 3 (got similar results with subs 1 & 2 both inverted and not inverted on sub 3, but then crossover integration with my mains was poor). The Red line on graph 2 was after time aligning as best I can with my very limited experience. I need to re-read the documentation on how to overlay impulse responses to do less guesswork. I think I'm close because REW listed the combined response as having the same delay as sub 2 by itself, which is the physically closest sub to the MLP. I got somewhat less gain than I expected overall by running 3 vs 2 subs, but did get a healthy increase in output (which means lower distortion since each sub has to work much less).
It struck me as odd that I had to invert phase on the VTF relative to the TNs, when I would have thought sub2 and sub 3 would need inversion relative to sub 1 since sub1 is in front of room and both sub 2 and sub 3 were in back corners of room. I took many more measurements than what is posted, but I chose the highlights, showing what having incorrect inversion and delay can do to response. As you can see from the graphs, my room has some challenges without EQ.
Those graphs are just the initial, lazy setup of throw a sub into an available corner and see what happens...
This setup has 1 TN1220 in the front left corner (only open corner in front of room), 1 TN1220 in back right corner, and the VTF-15H Mk2 in the back left corner of the room. Since I know the back right & front left corners sum together well, and I can't get the VTF into a front corner, I'm probably going to reposition the VTF in the right rear and use the 2nd TN to move around to try to boost the mid-bass suckout above 40Hz and even up the response.
I'm relatively happy with the non-EQ'd response below 40Hz, I just have to fix >40Hz stuff and am hoping moving the current rear TN will do that.
Do you think it would be better to fire the VTF into the wall, leaving 3-4" of space from grille to wall, or tuck the amp into the corner or will it likely not matter much? I suspect it won't make much difference as the wavelengths are so much longer than the length of the subwoofer, but I've found you have to test your assertions, and it almost seems like bass output in a real room only vaguely adheres to theory (or my almost complete lack of understanding said theory).
I also still need to play with port plugs, EQ switch, and Q settings on the VTF-15 as well.
I wish I would have placed a TN up front earlier considering what the low bass response is with a sub there. But, these are things one doesn't know they don't know until they measure it.